Conventional beam forming systems are often cumbersome to manufacture. In particular, conventional beam forming antenna arrays require complicated feed structures and phase-shifters that are impractical to be implemented in a semiconductor-based design due to its cost, power consumption and deficiency in electrical characteristics such as insertion loss and quantization noise levels. In addition, such beam forming arrays make digital signal processing techniques cumbersome as the operating frequency is increased. In addition, at the higher data rates enabled by high frequency operation, multipath fading and cross-interference becomes a serious issue. Adaptive beam forming techniques are known to combat these problems. But adaptive beam forming for transmission at 10 GHz or higher frequencies requires massively parallel utilization of A/D and D/A converters.
To provide a beamforming system compatible with semiconductor processes, the applicant has provided a number of integrated antenna circuits. For example, U.S. application Ser. No. 11/141,283 discloses a beamforming system in which an RF signal is distributed through a transmission network to integrated antenna circuits that include a beamforming circuit that adjusts the phase and/or the amplitude of distributed RF signal responsive to control from a controller/phase manager circuit. In a receive configuration, each beamforming circuit adjusts the phase and/or the amplitude of a received RF signal from the corresponding integrated circuit's antenna and provide the resulting adjusted received RF signal to the transmission network. Although such integrated antenna circuits consume a relatively small amount of power, transmission loss is incurred through the resulting RF propagation in the transmission network. To account for such loss, U.S. application Ser. No. 11/141,283 discloses a distributed amplification system such that RF signals propagated through the transmission network are actually amplified rather than attenuated. However, the transmission network introduces dispersion as well.
To avoid the dispersion introduced by an RF transmission network, an alternative integrated circuit (which may also be denoted as an integrated oscillator circuit) has been developed such as disclosed in U.S. Pat. No. 6,982,670. For example, each integrated oscillator/antenna circuit may include an oscillator such as a phase-locked loop (PLL) and a corresponding antenna and mixer. In such an embodiment, each PLL is operable to receive a reference signal and provide a frequency-shifted signal output signal that is synchronous with the reference signal. Should an integrated oscillator/antenna circuit be configured for transmission, its output signal is upconverted in the unit's mixer and the upconverted signal transmitted by the corresponding antenna. Alternatively, should an integrated oscillator/antenna circuit be configured for reception, a received RF signal from the unit's antenna is downconverted in the mixer responsive to the frequency-shifted output signal from the PLL. Although the integrated oscillator circuit approach does not have the dispersion issues resulting from propagation through a transmission network, the inclusion of an oscillator in each integrated oscillator circuit demands significantly more power than the transmission network approach.
Accordingly, there is a need in the art for beamforming systems compatible with semiconductor manufacturing processes having reduced power demands and reduced signal dispersion.